BF3 usage wise is no where near the 2GB it just allocates a ton.
So I can't imagine BF4 being beyond 2GB *especially on 1080*

I agree on the allocation being a ton; but it not being anywhere near it. I fly a helicopter so i really want smooth gameplay throughout; any stutter like that would cause me to die because i am flying so low and so fast to the ground. Thats why im just picky on being prepared because i hate dying to an fps drop or stutter because sometimes it can be very critical like in tight helicopter 1v1's when i am flying backwards and 10 feet off the ground and engaging a helicopter.

I hope it doesnt though. If Battlefield 4 only requires <2GB at 1080p then i might just get a third one for looks without even upgrading to Maxwell....and then carry myself out until the next Maxwell refresh.

I use the same card on my main machine, and even at 1440p with FXAA I have not once had a VRAM issue. At 1080p, I don't even come close, but I don't really use MSAA in MP games because for me, FXAA does a great job while keeping the framerate high.

Single card @ 1384/7688 clocks on a 1080p monitor w all Ultra + FXAA, I get 70-90fps with zero dips.
On any of my 1440p displays, same otherwise, I get around 60-70fps w a minimum of 49-55fps.

Seeing as BF4 is using the same engine just with some optimizations, I highly, HIGHLY doubt that you need anything more than you have.

I will say that I have found that SLI is very sensitive to CPU and Memory clocks, and with two highly OC'd 680 Lightnings + 3770K + 8-16GB Trident X 2400C9, I have seen as much as 30fps+ difference between the CPU/RAM at 4.4/1600 7-9-8-21 1T and 5.1/2666 10-11-11-32 1T. Any and I mean ANY bottleneck in your system will show itself with SLI, so OC the CPU as high as you can and get the memory clocked as high as possible with the tightest primary and tertiary timings it can pull.